1. Field of Invention
The present invention relates to optical scanning apparatus of light sources with different wavelengths that can be applied in an exposure light source for image development machines.
2. Related Art
The current development of optical scanning apparatus of light sources with different wavelengths is mostly used in optical laser printers. Please refer to FIG. 1 for the composing elements of laser printers, comprising of: laser sources (11, 12, 13), modulators (21, 22, 23), an optical beam combiner (30), a beam forming lens set (40), a rotary polygon (50) and an f-xcex8 lens (60).
The three laser light sources (11, 12, 13) generate three light beams with different wavelengths. The light beams pass through the modulators corresponding to the wavelengths (21, 22, 23), and they modulate an intensity of the light and the on/off time of each of the light sources. These light beams then pass through the optical beam combiner (30) and combine into a single beam.
Using the beam-forming lens set (40), the single beam left from the optical beam combiner (30) is focused, and the cross section shape of the beam is changed. The cross section shape can become oval, circular, or any other shape according to the needs of the users. The beam-forming lens set (40) can also make sure the light spots falling on the target (70) are the same size.
The light beam then passes through a rotary polygon (50). Through the rotation of the lens, the reflection angle of the light beam is changed as time goes by to scan the target (70). The light beam then passes through the f-xcex8 lens (60), so one of the beams scanning, at uniform speed, is then capable of constant linear velocity scanning and focusing.
Therefore, to make the light spots of the different wavelengths the same size on the target (70), a set of f-xcex8 lens (60) is designed. The corresponding light beams of three wavelengths can then focus, change the shape of the cross sections and achieve constant linear velocity scanning. However, the more light beams with different wavelengths, the more difficult it is to design the f-xcex8 lens (60), sometimes even impossible. The current f-xcex8 lens (60) is designed to allow linear scanning with constant speed for the wavelength of one of the light spots only, not for any other light spots. Under this condition, at any point in time, any two light spots emitted simultaneously (other than the central optic axis) cannot fall on the same position.
To simplify the described optical element in optical scanning apparatus for a plurality of wavelengths, the apparatus that is patented by U.S. Pat. No. 6,339,490 combines a rotary polygon (50) and f-xcex8 lens (60), shown in FIG. 2. The f-xcex8 lens (60) is installed on a rotating device (80) to emit the original rotating polygon (50), which still achieves linear scanning at a constant speed and simplifies the design of the optical element.
This known optical scanning apparatus is applied to laser printers, and used as the scanning technology for single wavelength light source. It cannot emit corresponding light spots of different wavelengths onto the same scanning position at the same time.
The invention is used to provide an optical scanning apparatus for a plurality of light sources of different wavelengths. By having the f-xcex8 lenses for each of the light sources of different wavelengths symmetric to its the central optic axis, the design for the f-xcex8 lens is simplified. Therefore, the light sources with different wavelengths can scan at the same constant linear velocity scanning.
The invention relates to optical scanning apparatus with a plurality of light sources of different wavelengths. All the light beams generated by different light sources pass through a collimator lens, a cylindrical lens, respectively, and then a beam combiner, to form single or multiple parallel beams. The single or multiple parallel beams of light pass through a reflective lens, and then through one or more f-xcex8 lenses, installed on the rotating apparatus. Different arrangements of the reflective lens corresponding to the f-xcex8 lenses achieve three different kinds of scanning: (1) light spots corresponding to different wavelengths scanning the same position in order (2) light spots corresponding to different wavelengths scanning different positions simultaneously (3) light spots corresponding to different wavelengths scanning the same position simultaneously.
Further scope of applicability of the present invention will become apparent from the detailed description given below. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.